The rabbit can regenerate holes punched through its external ear by convergent growth from the margins, including the replacement of its cartilaginous sheet. In the absence of ear cartilage, no regeneration occurs. The proposed research is designed to explore the role of cartilage in ear regeneration by substitution experiments. In one series, the sheet of cartilage will be replaced by scapula bone and a hole cut through the graft region to learn if regeneration can still occur. If so, will the scapula itself be replaced, someting it cannot do in situ? Other studies will focus on the possibility of substituting inert plastic implants for the ear cartilage to test their capacity for promoting regeneration, and to learn if the role of cartilage is more than just mechanical. The dependence of cartilage regeneration on its proximity to healing epidermis in rabbit ears deserves further investigation. By various surgical interventions, epidermal wound healing will be prevented altogether or separated spatially from the cut cartilage to determine if it is required to sustain or just to initiate chondrogenesis across a lesion. Finally, the remarkable capacities for regeneration in rabbit ears, will be compared with responses to similar experiments on the ears of other mammals to find out just how unique the rabbit really is.